Spanish HTT gene study reveals haplotype and allelic diversity with possible implications for germline expansion dynamics in Huntington disease.

We aimed to determine the genetic diversity and molecular characteristics of the Huntington disease (HD) gene (HTT) in Spain. We performed an extended haplotype and exon one deep sequencing analysis of the HTT gene in a nationwide cohort of population-based controls (n = 520) and families with symptomatic individuals referred for HD genetic testing. This group included 331 HD cases and 140 carriers of intermediate alleles. Clinical and family history data were obtained when available. Spanish normal alleles are enriched in C haplotypes (40.1%), whereas A1 (39.8%) and A2 (31.6%) prevail among intermediate and expanded alleles, respectively. Alleles ≥ 50 CAG repeats are primarily associated with haplotypes A2 (38.9%) and C (32%), which are also present in 50% and 21.4%, respectively, of HD families with large intergenerational expansions. Non-canonical variants of exon one sequence are less frequent, but much more diverse, in alleles of ≥27 CAG repeats. The deletion of CAACAG, one of the six rare variants not observed among smaller normal alleles, is associated with haplotype C and appears to correlate with larger intergenerational expansions and early onset of symptoms. Spanish HD haplotypes are characterized by a high genetic diversity, potentially admixed with other non-Caucasian populations, with a higher representation of A2 and C haplotypes than most European populations. Differences in haplotype distributions across the CAG length range support differential germline expansion dynamics, with A2 and C showing the largest intergenerational expansions. This haplotype-dependent germline instability may be driven by specific cis-elements, such as the CAACAG deletion.

Correction to: Genetic and clinical characterization of BRCA-associated hereditary breast and ovarian cancer in Navarra (Spain).

Following publication of the original article [1], the authors reported an error in Figure 2, where the color code of the text boxes is reversed. Figure 2-amended shows the correct color association between the text boxes and the different areas in the map: Navarra, neighbouring communities and other Spanish communities.

Genetic and clinical characterization of BRCA-associated hereditary breast and ovarian cancer in Navarra (Spain).

BACKGROUND: Genetic testing for BRCA1/2 genes is widely used as a strategy to reduce incidence and morbidity of hereditary breast and ovarian cancer (HBOC). The purpose of this study is to analyse the demographic and molecular characteristics of BRCA germline mutations in Navarra, Spain, and to investigate the clinical profile of hereditary and sporadic breast cancer (BC) and ovarian cancer (OC) in the Community. METHODS: The study includes 1246 individuals assessed for BRCA1/2 genetic testing in Navarra, during 2000-2016, and a cohort of BC (n = 4384) and OC (n = 561) from the population-based Navarra Cancer Registry. Distribution and molecular characteristics of BRCA1/2 mutations, as well as, comparative analysis of the clinical course, pathologic features and overall survival (OS) of patients in different risk groups were investigated. RESULTS: BRCA mutation detection rate was 16%, with higher proportion (63%) of BRCA2 families. Nineteen per cent of mutations were recurrent, one of which, BRCA2 c.6024dupG, showed high association to OC. BRCA carriers had double risk (95% CI = 1.04-4.33) of developing multiple malignancies than low risk families and were diagnosed at a much earlier age (16.6 and 11.7 years difference for BC and OC, respectively) when compared to the general population. For BC, BRCA carriers showed a more advanced histological stage, higher risk of bilateral neoplasms (OR = 4.3; 95% CI = 1.3-11.4, for BRCA2 carriers) and worse OS rate at 5-, 10- and 15- years, than women with sporadic tumors. For OC, over 70% of patients of all risk groups showed advanced stages at diagnosis, with the highest among BRCA1 carriers (91%). Furthermore, they also had higher probability of developing ovarian bilateral tumors (OR = 7.8, 95% CI = 1.7-55.7, for BRCA1 carriers) than the general population. Five-year OS rate was worse among women with sporadic OC than BRCA carriers, but it levelled out over the 15-year period. CONCLUSIONS: In addition to national similarities in the HBOC-BRCA1/2 associated mutational spectrum, we identified a recurrent BRCA2 pathogenic variant (c.6024dupG), highly associated to OC in Navarra. Carriers of BRCA1/2 mutations showed a more severe BC and OC phenotype and had a worse overall prognosis when compared to a large cohort of women with sporadic counterpart tumors.

Weaver Syndrome-Associated EZH2 Protein Variants Show Impaired Histone Methyltransferase Function In Vitro.

Weaver syndrome (WS) is a rare congenital disorder characterized by generalized overgrowth, macrocephaly, specific facial features, accelerated bone age, intellectual disability, and susceptibility to cancers. De novo mutations in the enhancer of zeste homolog 2 (EZH2) have been shown to cause WS. EZH2 is a histone methyltransferase that acts as the catalytic agent of the polycomb-repressive complex 2 (PRC2) to maintain gene repression via methylation of lysine 27 on histone H3 (H3K27). Functional studies investigating histone methyltransferase activity of mutant EZH2 from various cancers have been reported, whereas WS-associated mutations remain poorly characterized. To investigate the role of EZH2 in WS, we performed functional studies using artificially assembled PRC2 complexes containing mutagenized human EZH2 that reflected the codon changes predicted from patients with WS. We found that WS-associated amino acid alterations reduce the histone methyltransferase function of EZH2 in this in vitro assay. Our results support the hypothesis that WS is caused by constitutional mutations in EZH2 that alter the histone methyltransferase function of PRC2. However, histone methyltransferase activities of different EZH2 variants do not appear to correlate directly with the phenotypic variability between WS patients and individuals with a common c.553G>C (p.Asp185His) polymorphism in EZH2.

Somatic CAG repeat instability in intermediate alleles of the HTT gene and its potential association with a clinical phenotype.

Huntington disease (HD) is a neurodegenerative disorder caused by ≥36 CAGs in the HTT gene. Intermediate alleles (IAs) (27-35 CAGs) are not considered HD-causing, but their potential association with neurocognitive symptoms remains controversial. As HTT somatic CAG expansion influences HD onset, we hypothesised that IAs are somatically unstable, and that somatic CAG expansion may drive phenotypic presentation in some IA carriers. We quantified HTT somatic CAG expansions by MiSeq sequencing in the blood DNA of 164 HD subjects and 191 IA (symptomatic and control) carriers, and in the brain DNA of a symptomatic 33 CAG carrier. We also performed genotype-phenotype analysis. The phenotype of symptomatic IA carriers was characterised by motor (85%), cognitive (27%) and/or behavioural (29%) signs, with a late (58.7 ± 18.6 years), but not CAG-dependent, age at onset. IAs displayed somatic expansion that were CAG and age-dependent in blood DNA, with 0.4% and 0.01% of DNA molecules expanding by CAG and year, respectively. Somatic expansions of +1 and +2 CAGs were detected in the brain of the individual with 33 CAGs, with the highest expansion frequency in the putamen (10.3%) and the lowest in the cerebellum (4.8%). Somatic expansion in blood DNA was not different in symptomatic vs. control IA carriers. In conclusion, we show that HTT IAs are somatically unstable, but we found no association with HD-like phenotypes. It is plausible, however, that some IAs, close to the HD pathological threshold and with a predisposing genetic background, could manifest with neurocognitive symptoms.

Two novel disease-causing mutations in the CLRN1 gene in patients with Usher syndrome type 3.

PURPOSE: To identify the genetic defect in Spanish families with Usher syndrome (USH) and probable involvement of the CLRN1 gene. METHODS: DNA samples of the affected members of our cohort of USH families were tested using an USH genotyping array, and/or genotyped with polymorphic markers specific for the USH3A locus. Based on these previous analyses and clinical findings, CLRN1 was directly sequenced in 17 patients susceptible to carrying mutations in this gene. RESULTS: Microarray analysis revealed the previously reported mutation p.Y63X in two unrelated patients, one of them homozygous for the mutation. After CLRN1 sequencing, we found two novel mutations, p.R207X and p.I168N. Both novel mutations segregated with the phenotype. CONCLUSIONS: To date, 18 mutations in CLRN1 have been reported. In this work, we report two novel mutations and a third one previously identified in the Spanish USH sample. The prevalence of CLRN1 among our patients with USH is low.

Validation of diagnostic codes and epidemiologic trends of Huntington disease: a population-based study in Navarre, Spain.

BACKGROUND: There is great heterogeneity on geographic and temporary Huntington disease (HD) epidemiological estimates. Most research studies of rare diseases, including HD, use health information systems (HIS) as data sources. This study investigates the validity and accuracy of national and international diagnostic codes for HD in multiple HIS and analyses the epidemiologic trends of HD in the Autonomous Community of Navarre (Spain). METHODS: HD cases were ascertained by the Rare Diseases Registry and the reference Medical Genetics Centre of Navarre. Positive predictive values (PPV) and sensitivity with 95% confidence intervals (95% CI) were estimated. Overall and 9-year periods (1991-2017) HD prevalence, incidence and mortality rates were calculated, and trends were assessed by Joinpoint regression. RESULTS: Overall PPV and sensitivity of combined HIS were 71.8% (95% CI: 59.7, 81.6) and 82.2% (95% CI: 70.1, 90.4), respectively. Primary care data was a more valuable resource for HD ascertainment than hospital discharge records, with 66% versus 50% sensitivity, respectively. It also had the highest number of "unique to source" cases. Thirty-five per cent of HD patients were identified by a single database and only 4% by all explored sources. Point prevalence was 4.94 (95% CI: 3.23, 6.65) per 100,000 in December 2017, and showed an annual 6.1% increase from 1991 to 1999. Incidence and mortality trends remained stable since 1995-96, with mean annual rates per 100,000 of 0.36 (95% CI: 0.27, 0.47) and 0.23 (95% CI: 0.16, 0.32), respectively. Late-onset HD patients (23.1%), mean age at onset (49.6 years), age at death (66.6 years) and duration of disease (16.7 years) were slightly higher than previously reported. CONCLUSION: HD did not experience true temporary variations in prevalence, incidence or mortality over 23 years of post-molecular testing in our population. Ascertainment bias may largely explain the worldwide heterogeneity in results of HD epidemiological estimates. Population-based rare diseases registries are valuable instruments for epidemiological studies on low prevalence genetic diseases, like HD, as long as they include validated data from multiple HIS and genetic/family information.

Genotype-phenotype correlation in eight new patients with a deletion encompassing 2q31.1.

Microdeletions of the 2q31.1 region are rare. We present the clinical and molecular findings of eight previously unreported patients with overlapping deletions in 2q31.1. The patients have a variable clinical phenotype and present with developmental delay (7/8), growth retardation (5/8), seizures (2/8) and a craniofacial dysmorphism consisting of microcephaly (4/8), short palpebral fissures (7/8), broad eyebrows with lateral flare (7/8), low-set ears with thickened helices and lobules (5/8), and micrognathia (6/8). Additional congenital anomalies were noted, including limb abnormalities (8/8), heart defects (3/8), genital anomalies (3/8), and craniosynostosis (1/8). Six of these microdeletions, ranging in size from 1.24 to 8.35 Mb, were identified by array CGH, one larger deletion (19.7 Mb) was detected by conventional karyotyping and further characterized by array CGH analysis. The smallest region of overlap in all eight patients spans at most 88 kb and includes only the WIPF1 gene. This gene codes for the WAS/WASL interacting protein family member 1. The patients described here do not present with clinical signs of the Wiskott-Aldrich syndrome and the deletion of this single gene does not allow explaining the phenotype in our patients. It is likely that the deletion of different but overlapping sets of genes from 2q31 is responsible for the clinical variability in these patients. To further dissect the complex phenotype associated with deletions in 2q31, additional patients with overlapping phenotypes should be examined with array CGH. This should help to link particular phenotypes to specific genes, and add to our understanding of the underlying developmental processes.

Clinical manifestations of homozygote allele carriers in Huntington disease.

OBJECTIVE: Because patients homozygous for Huntington disease (HD) receive the gain-of-function mutation in a double dose, one would expect a more toxic effect in homozygotes than in heterozygotes. Our aim was to investigate the phenotypic differences between homozygotes with both alleles ≥36 CAG repeats and heterozygotes with 1 allele ≥36 CAG repeats. METHODS: This was an international, longitudinal, case-control study (European Huntington's Disease Network Registry database). Baseline and longitudinal total functional capacity, motor, cognitive, and behavioral scores of the Unified Huntington's Disease Rating Scale (UHDRS) were compared between homozygotes and heterozygotes. Four-year follow-up data were analyzed using longitudinal mixed-effects models. To estimate the association of age at onset with the length of the shorter and larger allele in homozygotes and heterozygotes, regression analysis was applied. RESULTS: Of 10,921 participants with HD (5,777 female [52.9%] and 5,138 male [47.0%]) with a mean age of 55.1 ± 14.1 years, 28 homozygotes (0.3%) and 10,893 (99.7%) heterozygotes were identified. After correcting for multiple comparisons, homozygotes and heterozygotes had similar age at onset and UHDRS scores and disease progression. In the multivariate linear regression analysis, the longer allele was the most contributing factor to decreased age at HD onset in the homozygotes (p < 0.0001) and heterozygotes (p < 0.0001). CONCLUSIONS: CAG repeat expansion on both alleles of the HTT gene is infrequent. Age at onset, HD phenotype, and disease progression do not significantly differ between homozygotes and heterozygotes, indicating similar effect on the mutant protein. CLASSIFICATION OF EVIDENCE: This study provides Class II evidence that age at onset, the motor phenotype and rate of motor decline, and symptoms and signs progression is similar in homozygotes compared to heterozygotes.

[Implementing a population-based rare diseases registry in Spain: the Navarre´s experience]. / Implementando un registro poblacional de enfermedades raras en España: La experiencia de Navarra.

In 2012, the Spanish Rare Disease Registries Research Network (Spain-RDR) was consolidated with the aim of creating a Spanish population-based Rare Diseases Registry. In order to achieve this, each of the 17 Spanish Regions had to develop its own regional registry with a common agreed methodology. The Population-based Rare Disease Registry of Navarre was created in 2013 and, since then, its implementation is been carried out. Navarre assumed the agreed list within the Spanish Network, which included 934 codes of the International Classification of Diseases, 9th Revision, Clinical Modification. Initially, the main data source used to capture cases was the Assisted Morbidity Registry of Navarre, which includes the Minimum Basic Data Set of every regional hospital discharges (both public and private). Afterwards, new data sources were been added and ongoing validation studies of captured cases were been developed. Population-based rare diseases registries are fundamental for the study and quantification of this type of diseases since the classification and coding systems used in the current healthcare information systems are very nonspecific. The analysis and cross-referencing of data among multiple data sources is essential to maximize case detection capacity. Due to the low prevalence of these diseases, a high false positives rate among the detected cases greatly affects the estimation of epidemiological indicators, which makes it necessary to validate the cases by verifying the diagnoses.

En 2012 se consolidó la Red Española de Registros de Enfermedades Raras para la Investigación (Spain-RDR) con el objetivo de crear un Registro poblacional español de Enfermedades Raras. Para conseguirlo, cada Comunidad Autónoma tenía que desarrollar su propio registro autonómico con una metodología común consensuada. El Registro Poblacional de Enfermedades Raras de Navarra se creó en 2013 y, desde entonces, se está desarrollando su implementación. Navarra asumió el listado consensuado dentro de la Red, que incluye 934 códigos de la 9ª revisión de la Clasificación Internacional de Enfermedades (modificación clínica). Inicialmente, la principal fuente de información utilizada para la captación de casos fue el Registro de Morbilidad Asistida de Navarra, que recoge el Conjunto Mínimo Básico de Datos de las altas hospitalarias (de centros públicos y privados) de la Comunidad Foral. Posteriormente se fueron añadiendo nuevas fuentes de información y desarrollando continuos estudios de validación de los casos captados. Los registros poblacionales de enfermedades raras son fundamentales para el estudio y cuantificación de este tipo de enfermedades ya que los sistemas de clasificación y codificación utilizados en los actuales sistemas de información sanitaria son muy inespecíficos. El análisis y cruce de datos entre múltiples fuentes es esencial para maximizar la capacidad de detección de casos. Al tratarse de enfermedades muy poco prevalentes, una tasa alta de falsos positivos entre los casos detectados afecta en gran medida la estimación de indicadores epidemiológicos, lo que hace necesario validar los casos verificando los diagnósticos.

Genotype-phenotype analysis in patients with giant axonal neuropathy (GAN).

Giant axonal neuropathy (GAN, MIM: 256850) is a devastating autosomal recessive disorder characterized by an early onset severe peripheral neuropathy, varying central nervous system involvement and strikingly frizzly hair. Giant axonal neuropathy is usually caused by mutations in the gigaxonin gene (GAN) but genetic heterogeneity has been demonstrated for a milder variant of this disease. Here, we report ten patients referred to us for molecular genetic diagnosis. All patients had typical clinical signs suggestive of giant axonal neuropathy. In seven affected individuals, we found disease causing mutations in the gigaxonin gene affecting both alleles: two splice-site and four missense mutations, not reported previously. Gigaxonin binds N-terminally to ubiquitin activating enzyme E1 and C-terminally to various microtubule associated proteins causing their ubiquitin mediated degradation. It was shown for a number of gigaxonin mutations that they impede this process leading to accumulation of microtubule associated proteins and there by impairing cellular functions.

Study of cerebral cavernous malformation in Spain and Portugal: high prevalence of a 14 bp deletion in exon 5 of MGC4607 (CCM2 gene).

OBJECTIVE: We aimed to study clinical, radiological and molecular genetic features of patients with cerebral cavernous malformations (CCMs) from the Iberian Peninsula. METHODS: We screened Krit1(CCM1), MGC4607(CCM2), and PDCD10(CCM3) by systematic SSCP and direct sequencing of coding exons in 48 nuclear families and 30 sporadic cases of CCM from Spain and Portugal. RESULTS: Screening of CCM patients detected nine different mutations in 19 families. We found four new mutations in Krit1. Three of them were caused by either a small insertion or deletion, which lead to frameshift and premature termination codons. We also found a missense L308H mutation located in a highly conserved sequence within the ankyrin domain of Krit1. In CCM2, we found a redundant 14 bp deletion in exon 5 of MGC4607 which predicts a truncated protein at residue 230. We did not find mutations in CCM3. CONCLUSIONS: Finding that the 14 bp deletion was present in eleven families from the Iberian Peninsula indicates a high prevalence of this mutation. This redundant CCM2 mutation is worth considering in molecular diagnosis and genetic counselling of cerebral cavernous malformations.

The p. R151C Polymorphism in MC1R Gene Modifies the Age of Onset in Spanish Huntington's Disease Patients.

The expansion of CAG repeats (≥36 CAG) in the HTT gene is the only known genetic cause of Huntington's disease (HD) and the main determinant of the course of the disease. The length of the expanded CAG repeats correlates inversely with the age of onset (AOO) but does not completely determine it. We investigated the role of the melanocortin 1 receptor (MC1R) gene as a modifier factor of AOO in 600 HD patients from Spain. We sequenced the entire region of the MC1R gene and analyzed all the nonsynonymous MC1R genetic variants with a minor allele frequency of at least 0.01 in HD patients. The variability in AOO attributable to the CAG repeats and MC1R polymorphisms was evaluated using a multiple linear regression model. We found that the loss-of-function p. R151C MC1R polymorphism has a significant influence on the AOO (P = 0.004; Bonferroni-corrected P = 0.032) which explains 1.42% of the variance in AOO that cannot be accounted for by the expanded CAG repeat. Our results suggest that the MC1R gene could modify the AOO in Spanish HD patients and encourage the evaluation of loss-of-function MC1R polymorphisms in other HD populations with a higher frequency of these MC1R polymorphisms.

Clinical manifestations of intermediate allele carriers in Huntington disease.

OBJECTIVE: There is controversy about the clinical consequences of intermediate alleles (IAs) in Huntington disease (HD). The main objective of this study was to establish the clinical manifestations of IA carriers for a prospective, international, European HD registry. METHODS: We assessed a cohort of participants at risk with <36 CAG repeats of the huntingtin (HTT) gene. Outcome measures were the Unified Huntington's Disease Rating Scale (UHDRS) motor, cognitive, and behavior domains, Total Functional Capacity (TFC), and quality of life (Short Form-36 [SF-36]). This cohort was subdivided into IA carriers (27-35 CAG) and controls (<27 CAG) and younger vs older participants. IA carriers and controls were compared for sociodemographic, environmental, and outcome measures. We used regression analysis to estimate the association of age and CAG repeats on the UHDRS scores. RESULTS: Of 12,190 participants, 657 (5.38%) with <36 CAG repeats were identified: 76 IA carriers (11.56%) and 581 controls (88.44%). After correcting for multiple comparisons, at baseline, we found no significant differences between IA carriers and controls for total UHDRS motor, SF-36, behavioral, cognitive, or TFC scores. However, older participants with IAs had higher chorea scores compared to controls (p = 0.001). Linear regression analysis showed that aging was the most contributing factor to increased UHDRS motor scores (p = 0.002). On the other hand, 1-year follow-up data analysis showed IA carriers had greater cognitive decline compared to controls (p = 0.002). CONCLUSIONS: Although aging worsened the UHDRS scores independently of the genetic status, IAs might confer a late-onset abnormal motor and cognitive phenotype. These results might have important implications for genetic counseling. CLINICALTRIALSGOV IDENTIFIER: NCT01590589.

Implementando un registro poblacional de enfermedades raras en España: la experiencia de Navarra / Implementing a population-based rare diseases registry in Spain: the Navarre's experience

En 2012 se consolidó la Red Española de Registros de Enfermedades Raras para la Investigación (Spain-RDR) con el objetivo de crear un Registro poblacional español de Enfermedades Raras. Para conseguirlo, cada Comunidad Autónoma tenía que desarrollar su propio registro autonómico con una metodología común consensuada. El Registro Poblacional de Enfermedades Raras de Navarra se creó en 2013 y, desde entonces, se está desarrollando su implementación. Navarra asumió el listado consensuado dentro de la Red, que incluye 934 códigos de la 9ª revisión de la Clasificación Internacional de Enfermedades (modificación clínica). Inicialmente, la principal fuente de información utilizada para la captación de casos fue el Registro de Morbilidad Asistida de Navarra, que recoge el Conjunto Mínimo Básico de Datos de las altas hospitalarias (de centros públicos y privados) de la Comunidad Foral. Posteriormente se fueron añadiendo nuevas fuentes de información y desarrollando continuos estudios de validación de los casos captados. Los registros poblacionales de enfermedades raras son fundamentales para el estudio y cuantificación de este tipo de enfermedades ya que los sistemas de clasificación y codificación utilizados en los actuales sistemas de información sanitaria son muy inespecíficos. El análisis y cruce de datos entre múltiples fuentes es esencial para maximizar la capacidad de detección de casos. Al tratarse de enfermedades muy poco prevalentes, una tasa alta de falsos positivos entre los casos detectados afecta en gran medida la estimación de indicadores epidemiológicos, lo que hace necesario validar los casos verificando los diagnósticos

In 2012, the Spanish Rare Disease Registries Research Network (Spain-RDR) was consolidated with the aim of creating a Spanish population-based Rare Diseases Registry. In order to achieve this, each of the 17 Spanish Regions had to develop its own regional registry with a common agreed methodology. The Population-based Rare Disease Registry of Navarre was created in 2013 and, since then, its implementation is been carried out. Navarre assumed the agreed list within the Spanish Network, which included 934 codes of the International Classification of Diseases, 9th Revision, Clinical Modification. Initially, the main data source used to capture cases was the Assisted Morbidity Registry of Navarre, which includes the Minimum Basic Data Set of every regional hospital discharges (both public and private). Afterwards, new data sources were been added and ongoing validation studies of captured cases were been developed. Population-based rare diseases registries are fundamental for the study and quantification of this type of diseases since the classification and coding systems used in the current healthcare information systems are very nonspecific. The analysis and cross-referencing of data among multiple data sources is essential to maximize case detection capacity. Due to the low prevalence of these diseases, a high false positives rate among the detected cases greatly affects the estimation of epidemiological indicators, which makes it necessary to validate the cases by verifying the diagnoses

Analysis of the molecular parameters that could predict the risk of manifesting premature ovarian failure in female premutation carriers of fragile X syndrome.

OBJECTIVE: To study three molecular parameters (number of CGG repeats, X-inactivation ratio, and expression of FMR1 mRNA) in premutation carriers of fragile X syndrome with and without premature ovarian failure (POF) to find differences between these two groups that could be useful in reproductive counseling. DESIGN: A retrospective clinical and molecular genetic study of 42 known premutation carriers of fragile X syndrome aged 40 years or older, 25 with POF and 17 without. A blood sample to obtain mRNA was taken from all of them. They all lived in five autonomous communities in northern Spain. RESULTS: Although the relationship among mRNA levels, X-inactivation ratio, and CGG repeats seems to be similar both in women with POF and in those without: in women with POF, the effect of the CGG repeats on the mRNA levels was statistically significant (P = 0.0437), but in women without POF, it was not (P = 0.0724). Moreover, we confirmed previous results on the nonlinear association between CGG repeat number and the manifestation of POF, showing that the likelihood of having POF was significantly higher with fewer than 100 CGG repeats compared with 100 or more CGG repeats (odds ratio = 13.09, P = 0.0240). CONCLUSIONS: Our present work suggests that mRNA and X-inactivation studies in blood are not relevant in predicting POF in female premutation carriers of fragile X syndrome. However, having a permutation of fewer than 100 repeats could represent a significant risk of POF.

Venezuelan kindreds reveal that genetic and environmental factors modulate Huntington's disease age of onset.

Huntington's disease (HD) is an autosomal dominant neurodegenerative disease caused by a triplet (CAG) expansion mutation. The length of the triplet repeat is the most important factor in determining age of onset of HD, although substantial variability remains after controlling for repeat length. The Venezuelan HD kindreds encompass 18,149 individuals spanning 10 generations, 15,409 of whom are living. Of the 4,384 immortalized lymphocyte lines collected, 3,989 DNAs were genotyped for their HD alleles, representing a subset of the population at greatest genetic risk. There are 938 heterozygotes, 80 people with variably penetrant alleles, and 18 homozygotes. Analysis of the 83 kindreds that comprise the Venezuelan HD kindreds demonstrates that residual variability in age of onset has both genetic and environmental components. We created a residual age of onset phenotype from a regression analysis of the log of age of onset on repeat length. Familial correlations (correlation +/- SE) were estimated for sibling (0.40 +/- 0.09), parent-offspring (0.10 +/- 0.11), avuncular (0.07 +/- 0.11), and cousin (0.15 +/- 0.10) pairs, suggesting a familial origin for the residual variance in onset. By using a variance-components approach with all available familial relationships, the additive genetic heritability of this residual age of onset trait is 38%. A model, including shared sibling environmental effects, estimated the components of additive genetic (0.37), shared environment (0.22), and nonshared environment (0.41) variances, confirming that approximately 40% of the variance remaining in onset age is attributable to genes other than the HD gene and 60% is environmental.